This application relates to avionic display systems, and more particularly to avionic display systems utilizing synthetic vision systems wherein runways, terrain, and other objects may be displayed in a three dimensional manner.
Aircraft cockpit displays often include a primary flight display (PFD) that displays, among other things, an artificial horizon line that indicates the aircraft's pitch and roll relative to the actual horizon. The PFD typically also displays the aircraft's current heading. In some PFD's, the artificial horizon line is displayed with a solid color above the horizon line—typically a shade of blue to represent the sky—and a solid color below the horizon line—typically a shade of brown to indicate the earth. Such displays do not provide any indication of the contours of the ground over which the aircraft is flying.
More advanced PFDs may include the feature of synthetic vision, which does provide images indicating the contours of the ground. With such displays, the ground is displayed in a three-dimensional manner so as to generally match what the pilot would see when he or she looks out the cockpit front windshield at the terrain in front of the aircraft. In order for the PFD to properly display the contours of the terrain in a three-dimensional manner, the PFD accesses data that defines the elevation of the ground at the areas being displayed. Such data is commercially available from multiple sources and may be uploaded to the PFD in multiple manners. Such data includes the height of the ground at thousands, if not millions, of data points distributed across one or more geographic areas. Such data may originate from one or more satellite measurements, one or more U.S. space shuttle missions, or from other sources.
Regardless of the source of the terrain height data, such data may, for example, include the height of the Earth's terrain for approximately every six arc-seconds of latitude and longitude over a particular geographic area, such as North America, or some other area. From this data, the PFD is able to visually re-create on its screen a rendering of the Earth's terrain that approximates the actual terrain of the Earth over which the aircraft is currently flying.
In addition to the contours of the terrain, synthetic vision displays may also display other ground-based landmarks, such as, for example, the runways at airports. In order for the PFD to display the runways at their proper locations and elevations, the PFD often consults an additional database that includes airport data which defines the location, elevation, and other features of airports and their associated runways. The PFD uses this data to render images on the PFD screen that approximate how the actual runway looks to the pilot when the pilot looks through the front windshield. The runway data typically come from a different source than the terrain data. For example, the runway data may be the result of manual surveying of each airport runway. Regardless of the source of the runway data, the runway data may include runway elevation information that either does not match the terrain height data, or that was measured at different locations than the measurements of the terrain height data.